4. The i3's 125 kilowatt electric motor, which revs at up to 11,400 rpm, drives the car's rear wheels. Lifting off the accelerator pedal instantly switches the motor into generator mode, feeding energy back into the battery.

5. The tiny petrol-powered 25 kilowatt range-extender engine is not connected to the wheels. Its sole job is to charge the battery. [...]

The i3 is the first of its kind. It is a fully electric car but can be equipped with a small petrol tank - not for running the motor but for running an electric generator that cuts in as needed to top up a flattening battery.